Method and apparatus of a sensor amplifier configured for use in medical applications

Abstract

A digital data bandpass filter process using digital signal processing processes raw digital data twice using distinct all-pass filters, wherein the two filters perform different frequency-dependent phase shifts of the digital content. The two filter output streams may be subtracted to remove out-of-band energy. The process produces lower levels of noise and conversion artifacts when used for filtering fixed-point data that may have low energy, and thus few non-zero bits, in the analog input signals, than conventional digital bandpass filters.

1 . A digital filter for fixed-point digital data, comprising:
 a first all-pass digital filter, wherein the first filter performs relative phase shift between constituent signal frequencies within data output from the analog-to-digital converter with a first predetermined profile of frequency-dependent relative phase shift, and wherein the first filter outputs phase-shifted data characterized by the first relative phase shift profile;   a second all-pass digital filter, wherein the second filter performs relative phase shift between constituent signal frequencies within data output from the analog-to-digital converter with a second predetermined profile of frequency-dependent relative phase shift, and wherein the second filter outputs phase-shifted data characterized by the second relative phase shift profile; and   a summer, wherein the summer accepts as inputs the outputs of the two all-pass filters, wherein the summer provides as an output the algebraic sum of the signals provided from the filters, wherein amplitude of content within at least a first predetermined frequency range reinforces through summing, and wherein amplitude of content within at least a second predetermined frequency range is canceled at least in part through summing.   
     
     
         2 . The filter of  claim 1 , wherein the summer output data is characterized by attenuation of at least one of relatively low-frequency signal content, relatively high-frequency signal content, and both relatively low and relatively high frequency signal content. 
     
     
         3 . The filter of  claim 1 , further comprising an analog-to-digital converter (ADC) interposed between analog electrical signal input circuitry and the digital filter. 
     
     
         4 . The filter of  claim 1 , further comprising:
 a first storage resource for digital data, wherein the first digital data storage resource is configured to accept ADC output data;   a second storage resource for digital data, wherein the second digital data storage resource is configured to accept data processed by the first all-pass digital filter; and   a third storage resource for digital data, wherein the third digital data storage resource is configured to accept data processed by the second all-pass digital filter.   
     
     
         5 . The filter of  claim 1 , further comprising:
 a digital signal processor (DSP), wherein the DSP is configurable to accept a sequence of digital data values as input, to implement at least one all-pass digital filter function, and to output a sequence of digital data values, wherein the output values are modified from the input digital data values by relative phase shift of signal component frequencies therewithin.   
     
     
         6 . The filter of  claim 3 , further comprising:
 a digital storage medium for a first set of instructions, wherein the first set of instructions includes at least data processing steps configured to apply a first relative phase shift to a plurality of signal component frequencies in a sequence of data elements;   a digital storage medium for a second set of instructions, wherein the second set of instructions includes at least data processing steps configured to apply a second relative phase shift to a plurality of signal component frequencies in a sequence of data elements; and   a digital storage medium for a third set of instructions, wherein the third set of instructions includes at least data processing steps configured to sum two digital data sequences and to scale the resultant.   
     
     
         7 . The filter of  claim 3 , further comprising:
 a passive analog front end, configured to accept as input a first plurality of distinct analog signals from a plurality of signal sources, and further configured to provide as output a second plurality of analog signals differing from the input signals principally in at least one of isolation, protection, and limiting;   an analog multiplexer (MUX), configured to accept from the passive analog front end the second plurality of analog signals, and further configured to accept a pattern of timing control signals, wherein the MUX further comprises a single analog signal output, wherein the single analog signal comprises successive samples of individual analog signals from the second plurality of analog signals, and wherein the successive samples are output in accordance with the pattern of timing control signals; and   a timing generator, configured to provide the pattern of timing control signals, wherein the pattern comprises a provision for selection between MUX input channels and a provision for initialization of ADC conversion actions.   
     
     
         8 . The timing generator of  claim 7 , further comprising:
 a set of control signals for the ADC, wherein the control signals for the ADC establish synchronization between the MUX and the ADC, wherein successive MUX output samples to the ADC are coupled thereto for a hold time compatible with ADC requirements, wherein the ADC control signals further trigger digitization of the successive MUX output samples, and wherein the ADC control signals further direct management of resulting digitized data at least in part.   
     
     
         9 . The filter of  claim 1 , further comprising an active analog front end configured to accept as input a first plurality of discrete analog signals, and further configured to provide as output a second plurality of discrete analog signals differing from the input analog signals principally in at least one of impedance, gain, isolation, and offset. 
     
     
         10 . The filter of  claim 1 , further comprising an Ethernet-compatible digital data transmitter, configured to transmit an indefinite stream of digital data elements derived from analog telemetry input signals. 
     
     
         11 . A filter for fixed-point digital data, comprising:
 first means for all-pass filtering an input having the form of a first succession of digital words comprising data signal samples, wherein the first means for all-pass filtering provides an output having the form of a second succession of digital words, wherein the phase of frequency components of the data signal samples is shifted differentially in accordance with predetermined parameters of the first means for all-pass filtering;   second means for all-pass filtering an input having the form of a first succession of digital words comprising data signal samples, wherein the second means for all-pass filtering provides an output having the form of a third succession of digital words, wherein the phase of frequency components of the data signal samples is shifted differentially in accordance with predetermined parameters of the second means for all-pass filtering, and wherein the phase shift of the second means for all-pass filtering differs from the phase shift of the first means for all-pass filtering;   means for summing the outputs of the first and second means for all-pass filtering, wherein the means for summing provides an output having the form of a fourth succession of digital words, wherein the difference in phase shift between the respective means for all-pass filtering differentially reinforces and cancels frequency components of the data signal samples.   
     
     
         12 . The filter of  claim 11 , further comprising means for scaling at least one of the input and the output of the means for summing. 
     
     
         13 . The filter of  claim 11 , further comprising means for converting analog signals to fixed-point digital form. 
     
     
         14 . The filter of  claim 13 , further comprising:
 means for accepting as analog front-end input a first plurality of discrete analog signals from a plurality of signal sources;   means for providing as analog front-end output a second plurality of discrete analog signals differing from the input signals principally in at least one of isolation, protection, and limiting;   means for accepting from the front end the second plurality of analog signals;   means for accepting a pattern of timing control signals;   means for providing as output a single multiplexed analog signal, wherein the multiplexed signal comprises successive samples of individual analog signals from the second plurality of analog signals, and wherein the samples are output in accordance with the pattern of timing control signals; and;   means for generating the pattern of timing control signals, wherein the pattern comprises a provision for selection between multiplexed input channels and a provision for initialization of conversion of a selected analog signal to digital form.   
     
     
         15 . The filter of  claim 11 , further comprising:
 means for storing a first digital data sequence comprising digitized and unfiltered analog data;   means for storing a second digital data sequence comprising data processed by the first all-pass digital filter; and   means for storing a third digital data sequence comprising data processed by the second all-pass digital filter.   
     
     
         16 . A method for filtering fixed-point digital data, comprising:
 applying a first all-pass filter function to an input having the form of a first succession of digital words comprising data signal samples, wherein the first filter provides an output having the form of a second succession of digital words, wherein the phase of frequency components of the data signal samples is shifted differentially in accordance with predetermined parameters of the first filter;   applying a second all-pass filter function to an input having the form of a first succession of digital words comprising data signal samples, wherein the second filter provides an output having the form of a third succession of digital words, wherein the phase of frequency components of the data signal samples is shifted differentially in accordance with predetermined parameters of the second filter, and wherein the phase shift of the second filter differs from the phase shift of the first filter;   applying a summing function to the outputs of the first and second all-pass filters, wherein the summing function provides an output having the form of a fourth succession of digital words, wherein the difference in phase shift between the respective filters differentially applies reinforcement to frequency components over at least a first frequency range and performs cancellation at least in part to frequency components over at least a second frequency range of the spectral content of the data signal samples.   
     
     
         17 . The method of  claim 16 , further comprising scaling at least one of the input and the output of the summing function. 
     
     
         18 . The method of  claim 16 , further comprising converting analog signals to fixed-point digital form. 
     
     
         19 . The method of  claim 18 , further comprising:
 accepting as analog front-end input a first plurality of distinct analog signals from a plurality of signal sources;   providing as analog front-end output a second plurality of analog signals differing from the input signals principally in at least one of isolation, protection, and limiting;   accepting from the front end the second plurality of analog signals;   accepting a pattern of timing control signals;   providing as output a single multiplexed analog signal, wherein the multiplexed signal comprises successive samples of individual analog signals from the second plurality of analog signals, and wherein the samples are output in accordance with the pattern of timing control signals; and   generating the pattern of timing control signals, wherein the pattern comprises a provision for selection between multiplexed input channels and a provision for initialization of conversion of a selected analog signal to digital form.   
     
     
         20 . The method of  claim 16 , further comprising:
 storing a first digital data sequence comprising digitized and unfiltered analog data;   storing a second digital data sequence comprising data processed by the first all-pass digital filter; and   storing a third digital data sequence comprising data processed by the second all-pass digital filter.